The present invention relates to a method of controlling a continuously variable transmission on a motor vehicle or the like, and more particularly to a method of controlling a continuously variable transmission in combination with the control of the throttle valve of an engine.
Heretofore, continuously variable transmissions have generally been controlled such that (a): the rotational speed of an engine coupled to the continuously variable transmission will reach a target speed, (b): the rate of change of the rotational speed of the engine will reach a target rate, and (c): the speed reduction ratio or transmission ratio of the transmission will reach a target ratio.
According to another method of controlling a continuously variable transmission, the rate of change of a speed reduction ratio is controlled, the rate being calculated as the sum of a component corresponding to a predicted acceleration that is calculated from the reserved power (the power which is available but not used) of an engine coupled to the transmission and a component corresponding to a target rate of change of the engine rotational speed (see, for example, Japanese Laid-Open Patent Publication No. 63-53343 and Japanese Patent Application No. 62-249590, both of which were filed by the applicant).
There is also known a method of simultaneously controlling a continuously variable transmission and a throttle valve of an engine coupled to the continuously variable transmission, so that the engine and a system for actuating the continuously variable transmission will be controlled to operate the engine at a minimum fuel consumption rate (see Japanese Patent Publication No. 61-8305, for example).
The conventional control methods described above do not present a problem insofar as the motor vehicle runs steadily or is gradually accelerated or decelerated. However, when the motor vehicle runs transiently, such as when the accelerator pedal is abruptly depressed to accelerate the motor vehicle, the rate of change of a controlled value until it reaches a target value may not necessarily best match the demand of the driver of the motor vehicle. Accordingly, under transient running conditions of the motor vehicle, the driver may not experience optimum feelings as to the driving conditions of the motor vehicle.